This invention relates to a system for communicating energy between two devices capable of relative linear or rotary motion, and more particularly, to a system for communicating data or power between a rotating frame and a fixed frame of a computed tomography ("CT") scanner.
With a conventional X-ray CT scanner, an X-ray tube is mounted on a rotating frame having a large diameter for the insertion of a patient. A radiation detector is set on the rotating frame opposite the X-ray tube to detect the radiation beams permeating the patient. The rotating frame is rotatably mounted on a fixed frame so that during operation the rotating frame and the fixed frame are in relative motion.
High-voltage power needed to operate the X-ray tube must be transmitted from the fixed frame to the rotating frame. Likewise, data collected by the radiation detector must be transmitted back from the rotating frame to the fixed frame. In addition, it is desirable that the rotating frame be able to rotate continuously.
The conventional solution is to interpose mechanical slip rings between the rotating frame and the fixed frame. Brushes mounted on the rotating frame contact the slip rings mounted on the fixed frame to allow electrical transmission of power or data. This mechanical interface, however, is subject to problems of wear and intermittent electrical contact. Furthermore, if data is transmitted at a high transmission rate, noise introduced by the electrical contacts may cause transmission errors.
An alternative solution is to use a single transmitter mounted on one of the devices, for example, the rotating frame, and a single reCeiver mounted on the other device, for example, the fixed frame, as shown in commonly-assigned application Ser. No. 07/316,991 entitled "Communication System for Transmitting Data," filed Feb. 28, 1989, and commonly-assigned application Ser. No. 07/317,026 entitled "Communication System for Transmitting Data," filed Feb. 28, 1989. With these arrangements, however, the path length between the input and the output may vary by half the circumference of the rotating frame. When transmitting data from the rotating frame of a CT scanner to the fixed frame of the CT scanner, the transmission rate may be so high that this variation in path length will cause phase errors to occur.
Multiple transmitters and receivers may be used, but this can be expensive. If many transmitters or receivers are needed, or if the effective range of operation of such transmitters and receivers must extend completely around the circumference of the rotating frame or the fixed frame, the cost is increased. Furthermore, there is a possibility of phase interference if two or more transmit-receive pairs are operating at the same time.
Similar problems arise when the transmitters and receivers are on two devices which must move laterally with respect to each other.